Flat-panel displays based upon many technologies, including liquid crystal, plasma, electro-luminescent (EL) display technologies, are well known in the art. Generally, these displays include a substrate having a display area. Individual light-emitting elements or subpixels are then arranged within this display area. Typically, a fixed and repeated distance in both the horizontal and vertical directions separates the light-emitting portions of each of these subpixels. This gap separating light-emitting portions of subpixels often includes electrical elements for providing drive signals to the light-emitting portions of the subpixels.
One of the characteristics critical to the performance of these flat-panel displays is the aperture ratio of the light-emitting portion of each subpixel, which is the portion of the area of each subpixel that emits light. This aperture ratio has a significant influence on the efficiency of displays that modulate light, such as liquid crystal displays, and has a significant influence on the lifetime of emissive displays, such as Organic Light Emitting Displays (OLEDs), in which each subpixel produces and emits light. To increase the aperture ratio, the size of electrical elements within the gap separating the light-emitting portions of the subpixels can be reduced. However, when these electrical elements are too small, they are unable to perform critical functions, such as distributing power among the subpixels within the display area. Within the display area, space is also required between the light-emitting portion of each subpixel and the electrical elements, as well as between many of the adjacent electrical elements within the display area, to prevent shorting and to allow tolerances for placement variability within the manufacturing process.
It is important that the size of many of the electrical elements is fixed for a particular display size. For instance, the size of a power bus is often determined with respect to the overall size of the display and the amount of current the power buss is required to distribute. Therefore, as the resolution of the display is increased and more subpixels are designed to fit within the display area, the aperture ratio of the light-emitting portions of these subpixels decreases as the resolution of the display is increased. This constraint directly conflicts with the display market's demand for high-resolution displays.
Typically, the subpixels within flat-panel displays are equally separated in the horizontal and vertical direction as each subpixel is formed from the same or very similar arrangements of a light-emitting portion and electrical elements. This arrangement is replicated over the entire display area. It is accepted in the art that imaging artifacts are reduced by this regular, repetitive arrangement of light-emitting and non-light-emitting subpixel portions. This repetitive arrangement is typically employed even in full-color displays that have different subpixels for emitting each of three or more colors of light.
It is known in the art to employ pixel arrangements in which the same subpixel layout is not replicated across the entire display. For example, Miyajima in US Publication No. 20020057266, entitled “Active Matrix Display Device” describes a liquid crystal display wherein a power line is shared between two rows of liquid crystal subpixels. In this arrangement the same subpixel arrangement is not repeated across the entire substrate but instead even and odd rows of subpixels within the display area each have a different layout and a different separation. This arrangement has the advantage that because power lines are shared among rows of subpixels, the size of the power buss is reduced and the tolerance required around one of the power busses is eliminated, allowing the aperture ratio of the liquid crystal modulators to be increased. However, within this arrangement, Miyajima teaches a method to maintain equal space between the light-emitting portions of the subpixels to avoid imaging artifacts. It is worth noting that although even and odd rows of subpixels had different arrangements, this arrangement is specific to displays having alternate rows of subpixels with different arrangements.
Winters in U.S. Pat. No. 6,771,028, entitled “Drive circuitry for four-color organic light-emitting device”, Winters et al. in U.S. Pat. No. 7,382,384 entitled “OLED displays with varying sized pixels”, and Cok et al. in US Publication No. 20070176859, entitled “EL device having improved power distribution” each discuss EL display pixel arrangements in which power busses or other electrical elements are shared among groups of four subpixels, which form a four-color pixel. Once again, this arrangement has the advantage of sharing power busses or other electrical elements between two adjacent rows or columns of subpixels. Sakamoto in U.S. Pat. No. 7,368,868 entitled “Active Matrix Organic EL Display panel” discusses an EL display having a different-sized gap between subpixels within one direction than in the other direction. Each of these disclosures within the EL display art, however, shows or describes pixel arrays in which the distance between all pixels is equal along at least one direction, wherein a pixel is the smallest possible repeating group of subpixels containing all colors of subpixels within the display.
Displays or sensors having variable-sized and variable-spaced light-collection or light-emitting elements are also known. For example Berstis in U.S. Patent Application Publication No. 20030184665, entitled “Anti-moire pixel array having multiple pixel types” discusses of one such arrangement. However, this disclosure does not discuss or describe the routing of electrical elements within this random array. The requirement for the electrical elements and the light-emitting portion of the subpixels to share space within the display area, as well as manufacturing yield and performance considerations which dictate the need for the electrical elements to nearly follow a regular grid, makes such an arrangement impractical for most flat-panel display applications.
As the resolution of a display increases further, additional increases in aperture ratio are necessary to improve the efficiency and lifetime of flat-panel displays. This increase in aperture ratio should be achieved without producing undesirable image artifacts that degrades the image quality of the display to an unacceptable level.